Financings and Capitalization (Narrative) (Details) - USD ($)	1 Months Ended				9 Months Ended		24 Months Ended
	Oct. 29, 2020	Sep. 30, 2020	Apr. 30, 2020	Mar. 31, 2020	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019	Jul. 31, 2020
Financing And Capitalization [Line Items]
Principal balance		$ 2,334,000,000			$ 2,334,000,000
Amount available for dividend payments		$ 5,300,000,000			5,300,000,000
Common stock dividends from Consumers					449,000,000
Stock offering program maximum value			$ 500,000,000
Proceeds from settlement of forward contracts					$ 107,000,000	$ 9,000,000
Settlement required (in shares)		538,335			538,335
Consumers Energy Company
Financing And Capitalization [Line Items]
Principal balance		$ 1,534,000,000			$ 1,534,000,000
Unrestricted retained earnings		1,600,000,000			1,600,000,000
Consumers Energy Company | Commercial Paper
Financing And Capitalization [Line Items]
Short-term debt, authorized borrowings					500,000,000
Short-term debt		0			$ 0
Forward Contracts
Financing And Capitalization [Line Items]
Forward sales contracts aggregate price		$ 52,000,000					$ 250,000,000
Settlement of Forward Contracts
Financing And Capitalization [Line Items]
Settlement of forward contract issued (in shares)				2,017,783
Forward contract settlement (in dollars per share)				$ 47.95
Proceeds from settlement of forward contracts				$ 97,000,000
Tax Exempt Revenue Bonds | Tax Exempt Revenue Bonds Due 2035 | Consumers Energy Company
Financing And Capitalization [Line Items]
Debt repurchased								$ 35,000,000
Subsequent Event | First Mortgage Bonds Due October 2070 | Consumers Energy Company
Financing And Capitalization [Line Items]
Principal balance	$ 127,000,000
London Interbank Offered Rate (LIBOR) | Subsequent Event | First Mortgage Bonds Due October 2070 | Consumers Energy Company
Financing And Capitalization [Line Items]
Basis spread on variable rate	0.30%
Interest rate floor	0.00%